The measure failed to clear a 60-vote threshold on Thursday afternoon, 54-42.

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Senate Majority Leader Harry Reid (D-Nev.) quickly moved to hammer Republicans and tie them to Charles and David Koch, billionaire brothers who back national conservative political operations.

“Senate Democrats want a government that works for all Americans — not just the richest few. Today, Senate Republicans clearly showed that they would rather sideline hardworking families in order to protect the Koch brothers and other radical interests that are working to fix our elections and buy our democracy,” Reid said after the vote.

The constitutional amendment would allow Congress and state lawmakers to override recent Supreme Court decisions that have struck down campaign finance laws previously passed by Capitol Hill — language that Republicans argued amounts to an attack on the Bill of Rights.

“The proposed amendment would restrict the most important speech the First Amendment protects, core political speech,” said Sen. Chuck Grassley (R-Iowa) on Wednesday. “It’s hard to imagine what would be more radical than the Congress passing a constitutional amendment to overturn a dozen Supreme Court decisions that have protected individual rights. Free speech would be dramatically curtailed.”

The failure of the proposal followed a surprising result on Monday, when the measure advanced past an initial filibuster despite broad GOP opposition to the measure.

Grassley and two dozen other Senate Republicans voted to advance the bill to blunt Democrats’ plans to hold a second round of campaign-flavored Democratic votes on proposals aimed at raising the minimum wage, overturning the Hobby Lobby Supreme Court decision, chipping away at gender pay disparities and reforming the student loan system.

The Senate has only a few more days in session — and Democratic aides said it will be difficult for the chamber to get to all the Fair Shot Agenda votes they hoped to hold this month, given Republican votes to advance the constitutional amendment Monday and the pay-equity bill on Wednesday, both of which consumed days of debate time. The next Senate vote is on Monday to end debate on the pay-equity bill — which will likely fail.

Sen. Chuck Schumer (D-N.Y.), the Democrats’ top message man, said voters will not forget Republicans’ rejection of an amendment that Democrats argue would get “dark money” out of politics and broadly drives GOP policies.

“The constitutional amendment is related to every one of our priorities, because you need to have fair elections in order to give middle-class families a fair shot. We’ll tie each issue, whether it be paycheck fairness or college loans, back to the reason these [Fair Shot Agenda] bills don’t pass, which is our campaign finance system,” Schumer said.